Road surfacing



Patented Jan. 23, 1940 UNITED- STATES ROAD SURFACING Carl Alexander Agthe,

Zurich, Switzerland, as-

signor to J. R. Geigy A. G., Basel, Switzerland No Drawing. Application December 14, 1938, Serial No. 245,770. In Switzerland December 23,

2 Claims.

Road surfacing materials consisting of small stone and tar have the disadvantage of remaining soft after their laying, on tothe road, until the tar hasthickened sufliciently by the partial evaporation of its oils and by oxidation and polymerisation. It usually takes several days until the tar coatinghas become hard and during this peri- 0d the road surface suffers through indentation by vehicles pasing over it.

Tar coatings of sufiicient resistance can be obtained by the use of tars which are semi-solid to solid at atmospheric temperature. In this case however the tar made thinly fluid by heating must be mixed with hot stones and the mixed materials.

spread and rolled while in hot condition. After cooling a hard layer is obtained. This way of working which is often used for asphalt and bitumen layers, does not give good results with tar because a tar thickened up to a solid consistency gives a brittle layer when admixed with stones. The insufficient adhesiveness of highly thickened tar is still further reduced when the tar has been heated to the high temperature necessary to enable the separate fragments of the stones tobe properly coated.

It has now been found that it is possible to produce tarred layers without the stated disadvantages if a mixture of small stone such as chippings or sand, it may be with additions such as mineral fillers, cement and so forth, is first prepared with the usual fluid to viscous street tar, and a stiffening of the mass is then effected by means of an admixed pulverized condensation product obtained by condensing with an aldehyde, preferably formaldehyde, a pine wood pitch of substantial insolubility in petroleum hydrocarbons, being the residue from the extraction of fine wood oil with a solvent, and described in the U. S. Patent 2,115,496. In this use the said finely pulverized condensation product very easily dissolves in tar at atmospheric temperatures a is more easily coated by a fluid tar than by a pasty to solid binding agent. I

According to the present process the usual street tar of thin fluid, to thick fluid consistency can be used for coating the stone material. Tar bitumen mixture, oxidized tars such as so-called weather tar and tar with refining agentscan also. be used. If the thin fluid tar is chosen the coating of the stonecan be efiected in the cold but with the use of thickly fluid tar the mixture must be prepared hot. The pulverized condensation product is best added directly tothe cold or hot mixture in the mixing chamber. If the hot process is used there is no danger of the tar sufiering too high a temperature because such tars can be chosen for the present process which by heating to temperatures below 120 C. are already so thinly fluid that they can easily be mixed with the stone. The pulverized condensation product can also be added subsequently to a prepared mixture. It is only important that the powder should come into contact with fresh tar mixture and not with mixture whichhas been laid for some time. To achieve the desired effect care must also be taken that the powder used has as fine and uniform a degree of sub-division as possible.

The pulverized condensation product can also be used mixed with inorganic or organic powders as for example mineral fillers, cement, ground brown or hard coal and similar materials.

Example 1 Example 2 To 200 kg. of stone consisting of two parts by 7 volume of 3-6 mm. chippings and three parts by volume of 0-3 mm. broken sand, after the addition of 13 kg. of lime powder, 20 kg. of a thin fluid tar having a viscosity of about 3 sec. measured at about 30 C., are added when heating and then while stirring 2 kg. of a mixture of two parts of pulverized condensation product of the aforesaid nature and three parts of lime powder are strewn on.

Example 3 To 200 kg. of stone consisting of two parts by volume of 5-8 mm. chippings, 2 parts by volume of 0-3 mm. broken sand and half part by volume of pit sand, kg of mineral filler are added and thereupon 14 kg. of street tar having a viscosity of 200-300 sec. measured at30 C. are stirred into a homogeneous mixture, the stone material being heated to 60-80 C. and the tar to about 100 C. To this is added 0.8 kg. of a mixture of two parts of the aforesaid pulverized condensation product and then intermixed by means of hoeor ploughlike implements with the aforesaid powdered condensation product. Inversely it is also possible to first incorporate to the stone orsand'layer the aforesaid powdered condensation product and to thereupon add the fluid tar thereto.

It is already known to produce macadam layers by coating broken stone. first with a fluid or semi-fluid binding agent and then with a resin or pitch in dust or powder form. In contradistinction the condensation product used according to the invention does not serve as a binding agent as is apparent from the very small quantity used of less than 1%. In Example 3 the quantity of the aforesaid condensation product amounts to but 0.14% calculated on the mixture. In the present process only the fluid to thick fluid tar which is added direct to the stone material, acts as a binder. The sole function of the aforesaid condensation product is to stiffen the mixture.

What I claim is:

1. A process for stiffening road making layers of small stone and tar, characterized in that a pulverized condensation product obtained by condensing with an aldehyde a pine wood pitch of. substantial insolubility in petroleum hydrocarbons, being the residue from the extraction of pine wood oil with a solvent, is added to the road making mixture before or during its laying.

2. A process according to claim 1, characterized in that the aforesaid pulverized condensation product is used mixed with organic or inorganic powders.

CARL ALEXANDER AGTI-IE. 

